function y = IF_calculate (IF_PU,B_PU,Sub_num,B_SU)

for i=1:Sub_num/2
    
    y(i) = IF_PU - B_PU/2 -Sub_num*B_SU/2+ B_SU/2 + B_SU*(i-1);
    
end

for i = Sub_num/2+1: Sub_num
    
    y(i) = y(i-Sub_num/2) + B_PU + Sub_num/2*B_SU;
    
end